1. Field of the Invention
This invention relates to a substrate and an organic electroluminescence device using the substrate, and more particularly, to a substrate with a plurality of surface energies which can be manufactured at low cost and with a thinner coating than conventional substrates, and an organic electroluminescence device using the substrate.
2. Description of the Related Art
An inkjet printing process is an important structuring process for the manufacture of full-color displays using light-emitting polymers (LEPs). In the inkjet printing process, a small amount of a polymer solution is deposited onto a suitable substrate. The spatial dissolution of the polymer solution is predominantly influenced by the surface characteristics of the substrate. To avoid color mixing of the so called “pixel surface”, wetting using deposited polymer ink should be carried out only in a zone which is envisioned for a light-emitting pixel.
Areas of a substrate surface with a high surface energy allow ink for printing to flow, whereas areas with a low surface energy act as a barrier to ink flow. To obtain a film having a homogenous coating thickness, it is advantageous for a portion of the substrate beyond a boundary of a pixel surface of an organic light-emitting diode (OLED) to have a high surface energy. If the portion of the substrate beyond the boundary of the pixel surface has a high surface energy, the formed film has a homogenous thickness up to the boundary and the coating thickness noticeably declines outside an active zone in the vicinity of the barrier.
A desired contrast in surface energy can be achieved in different ways and by different methods.
One known approach is described in the EP 0989778 A1. In this approach, a substrate surface with a contrast of surface energies is formed by means of a suitable selection of materials for forming the substrate surface.
EP 0989778 A1, for example, describes a two-coating structure of a surface. By means of a suitable plasma surface treatment, an upper coating can be provided with a low surface energy while a lower coating, because of its chemical nature, receives a high surface energy with the same treatment. The lower coating is typically manufactured from inorganic materials such as silicon oxide/nitride.
In this approach, the inorganic coating acts as a boundary zone with a high surface energy and facilitates the deposition of homogenous polymer films by means of inkjet printing. However, for deposition and structuring of inorganic coatings, various processes typically used in the semi-conductor industry should be performed. For example, to attain the inorganic coatings, separation, sputter processes and gas phase processes such as PECVD (Plasma Enhanced Chemical Vapor Deposition) may be used.
However, these processes are expensive, and thus reduce the cost efficiency that can be gained by using OLED technology. Moreover, the second coating layer has a surface topography such that the areas with low surface energy (hereinafter called “separators”) are spaced apart a predetermined height from the substrate surface. As a result of this height profile, the separated polymer film can form an undesirable thickness profile.
JP09203803, for example, describes a chemical treatment on a substrate surface having a photo-resist formed thereon. The photo-resist is exposed using a mask and then developed. In the resulting structure, the areas with the photo-resist have a low surface energy while areas without the photo-resist have a high surface energy. The flanks of the photo-resist structure have a mean surface energy, and thus can avoid an abrupt transition in surface energy to a certain degree. However, the flanks do not represent a boundary zone with a freely selectable surface energy and geometry because the spatial dissolution capacity of the inkjet printing process disadvantageously declines through areas with a mean surface energy.
JP09230129, for example, describes a two-stage treatment on a substrate surface. Initially, the substrate surface has a low surface energy, but the surface energy gradually increases at a predetermined portion of the surface which is treated with short-wavelength light. However, according to this method, contrast of a surface energy is limited and an exposure time is prolonged, making mass production difficult.